The present invention relates to a two-way paging system capable of calling users carrying pagers by radio, and allowing them to send messages from their pagers to base stations. In the following description, a signal from a pager to a base station is referred to as an xe2x80x9cupward signalxe2x80x9d.
FIG. 1 is a block diagram showing a two-way paging system, which applies a direct sequence spread spectrum scheme to transmit upward signals from pagers to base stations. The paging system comprises a central station 3 connected to a communications network 2; a plurality of (n) base stations 7-1-7-n connected to the central station 3; and pagers 8-1 and 8-2 capable of carrying out radio communications with the base stations 7-1-7-n.
The central station 3 comprises an accepting unit 10, encoder 11, spreading code assigner 12 and line terminal unit 13. The accepting unit 10 is connected to the communications network 2, receives paging request signals from the communications network 2, and supplies them to the encoder 11. The encoder 11 converts the paging request signals and code notification signals into paging signal sequences. The code notification signals are output from the spreading code assigner 12 to notify the pagers of spreading codes for the upward signals. The line terminal unit 13 delivers the paging signal sequences to corresponding base stations. The line terminal unit 13 also receives the upward signals sent from the pagers through the base stations, collects them, and supplies them to the accepting unit 10. Thus, the accepting unit 10 notifies the telephone 1 or computer terminal 9 of a paging response through the communications network 2.
The base stations 7-1-7-n each comprise a line terminal unit 20, transmitter 21, spreading code memory 25 and receiver 24. The line terminal unit 20 receives the paging signal sequences from the central station 3, and transfers them to the transmitter 21. The transmitter 21 converts them to radio signals (electromagnetic waves), and transmits them at a frequency F1. The receiver 24 in each of the base stations 7-1-7-n receives the upward signals from the called pagers that are detecting the paging signals addressed thereto. The receiver 24 uses a plurality of spreading codes prestored in the spreading code memory 25 for despreading these upward signals. The received upward signals are transmitted through the line terminal unit 20 to the central station 3, so that it sends the response information to the telephone 1 or computer terminal 9 via the communications network 2.
Next, the operation will be described for paging the pager 8-1 or 8-2 from the fixed telephone 1 or computer terminal 9. The user inputs to the telephone 1 or computer terminal 9 the called number of the pager 8-1 or 8-2, and a message if there is any. The input information is sent to the central station 3 through the communications network 2 as a paging request signal. In the central station 3, the encoder 11 converts into the paging signal sequence the paging request signal from the accepting unit 10 and the code notification signal supplied from the spreading code assigner 12 to notify the called pager of the spreading code. The line terminal unit 13 transmits it to the base stations 7-1-7-n. The base stations 7-1-7-n each convert it to a radio signal (electromagnetic wave), and transmit it simultaneously to their own radio zones 5-1-5-n at the same frequency F1. The pagers 8-1 and 8-2 each receive the radio signal at the predetermined frequency F1, and informs the user of the pager when they detect the paging signal calling them. After that, the pager 8-1 or 8-2 sends to the base stations a paging response it produces by the direct sequence spread spectrum modulation using the spreading code that is defined by the code notification signal received in conjunction with the paging signal. The base station in the radio zone in which the pager is located despreads the upward signal using the spreading code prestored in the spreading code memory 25, and transmits it to the central station 3 (in the example as shown in FIG. 1, the base station 7-1 receives the upward signal transmitted from the pager 8-1, and the base station 7-2 receives the upward signal transmitted from the pager 8-2). Thus, the central station 3 notifies the telephone 1 or computer terminal 9 via the communications network 2 that the pager accepts the call.
FIG. 2 illustrates a structure of the paging signal sequence sent from the base stations. The paging signal sequence is based on the signal structure shown in the RCR STD-43 standard worked out by Association of Radio Industries and Businesses in Japan. In this signal structure, the paging signal sequence consists of frame sequences each of which includes m successive frames as shown in FIG. 2(a). Each frame has a signal length of Tf, and consists of a synchronization signal and p subframes as shown in FIG. 2(b) which illustrates the i-th frame (1xe2x89xa6ixe2x89xa6m) as an example, which will be called xe2x80x9cframe ixe2x80x9d from now on. Here, p represents the number of times of transmissions of the same paging signal. Each subframe of the frame i includes an address field, vector field and message field: The address field consists of qji (1xe2x89xa6jxe2x89xa6p) address signals; the vector field consists of qji vector signals corresponding to the address signals; and the message field consists of qji message signals corresponding to the address signals as shown in FIG. 2(c) which illustrates the p-th subframe. A vector signal k (1xe2x89xa6kxe2x89xa6qji) indicates the start point and end point of a message signal k corresponding to an address signal k. With such a signal structure, the code notification signal is affixed to an initial position of each message signal in the message field.
Thus, the subframe p in the frame i in the paging signal sequence has qpi paging signals inserted thereinto, wherein k-th (1xe2x89xa6kxe2x89xa6qpi) paging signal is provided with the code notification signal Cuk indicative of the spreading code used for generating the upward signal by the direct sequence spread spectrum modulation. When the pager, to which the frame i is assigned to be received, detects its own paging signal in the frame i during the transmission period Tf beginning from time t0, it starts to transmit the response upward signal corresponding to the paging signal from time t0+Tf at the earliest. FIG. 2(d) illustrates an example in which it transmits the upward signal during time t0+2Tf-t0+3Tf considering the processing delay and the like required for receiving and transmitting the signal.
FIG. 3 is a block diagram illustrating a configuration of the pager. It comprises a receiver 30, controller 31, speaker 32, driver 33, display 34 and transmitter 35. The transmitter 35 is a direct sequence spread spectrum modulation transmitter. The receiver 30 is brought into a receiving state only during a receiving period of one or more preassigned frames among the paging signal sequences transmitted from the base station, and receives the frames. This technique, which is called an intermittent receiving method, can prolong the life of the battery of the pager. The controller 31 checks whether its own paging signal is present or not in the received frame, and notifies, if it is detected, the user that a call takes place, by a beep from the speaker 32 or some other alarms. If the paging signal includes a message, the controller 31 displays it on the display 34 via the driver 33. Then, the controller 31 supplies the transmitter 35 with a response upward signal corresponding to its own paging signal detected, together with a spreading code uniquely determined by the code notification signal contained in the paging signal. The transmitter 35 carries out, using the spreading code fed from the controller 31, the direct sequence spread spectrum modulation of the upward signal which is also fed from the controller 31, and transmits it to the base station. In this case, the frequency Fb for transmitting the upward signal is uniquely predetermined from the frequency F1 for receiving the paging signal.
FIG. 4 illustrates an example of the upward signal composed of the synchronization signal, pager ID (identification) signal and response information acknowledging reception of the paging signal.
If two pagers, which receive the same forward signal frequency Fl, receive paging signals transmitted in the same frame, they will simultaneously transmit their upward signals using the same frequency Fb. If the two pagers belong to different radio zones as shown in FIG. 1, the two upward signals will be received without collision. In contrast with this, the upward signal from the pager 8-2 can collide with that from the pager 8-1, if it arrives at the base station 7-1 from the pager 8-2 located in the contiguous radio zone 5-2, or if it arrives at the base station 7-1 because the pager 8-2 moves to the radio zone 5-1 after receiving the paging signal sequence. Even in such a case, however, the upward signals can be received distinctly because the spreading codes determined by the code notification signals differ from each other, and are all known by the base station 7-1 because they are prestored in the spreading code memory 25.
The pager with the function to transmit the upward signal is applicable not only to respond to the paging signal, but also to transmit information to another pager or a telephone or computer connected to the communications network, or to transmit information for its location registration. Such transmitting operation of the pager other than transmitting the response upward signal is referred to as xe2x80x9cpager initiativexe2x80x9d from now on.
An object of the present invention is to provide a two-way paging system enabling the base station to receive the response upward signal acknowledging reception of the paging signal, and the pager initiative upward signal, independently.
There is provided a paging system having one or more base stations for transmitting to a radio zone a paging signal sequence, and one or more pagers for receiving at least one paging signal of the paging signal sequence transmitted from the one or more base stations,
the pagers each comprising:
response means for transmitting, when the paging signal sequence received includes a paging signal addressed to the pager, a response signal acknowledging reception of the paging signal, through direct sequence spread spectrum modulation; and
initiative transmission means for transmitting a pager initiative signal through direct sequence spread spectrum modulation using a spreading code different from that used by the response means, and
the base stations each comprising:
receiving means for receiving, from the response means and the initiative transmission means of the pagers, signals that undergo the direct sequence spread spectrum modulation.
According to the present invention, different spreading codes are assigned to the response upward signal acknowledging the reception of the paging signal and to the pager initiative upward signal. This enables the base station to receive the two types of upward signals independently even if they collide with each other, thereby improving their transmission quality.
Here, the paging signal sequence transmitted from the base stations may include information designating a spreading code used for transmitting the response signal;
each of the pagers may further comprise code detection means for detecting from the paging signal sequence the spreading code designated; and
the response means of the pager may carry out the direct sequence spread spectrum modulation using the spreading code the code detection means detects.
The pagers may comprise a spreading code memory for storing a second group of spreading codes different from a first group of spreading codes used by the response means; and
the initiative transmission means may carry out initiative transmission by selecting a spreading code from the spreading code memory.
The pagers may comprise a spreading code memory; and
the initiative transmission means may carry out an initiative transmission by selecting from the spreading code memory a spreading code other than the spreading code the code detection means detects.
The base stations may further comprise a spreading code memory that stores entire spreading codes used; and
the receiving means may receive signals from the response means and the initiative transmission means in each of the pagers by using the spreading code memory.
The base stations may further comprise a memory for storing the spreading codes designated for the pagers, and a spreading code memory that stores the second group of the spreading codes; and
the receiving means may receive, using the memory and the spreading code memory, signals from the response means and the initiative transmission means in the pagers.
The base stations may further comprise a memory for storing spreading codes designated for the pagers, and a spreading code memory that stores entire spreading codes use; and
the receiving means may receive, using spreading codes from the memory and spreading codes from the spreading code memory excluding those stored in the memory, the signals from the response means and the initiative transmission means in each of the pagers.
The spreading codes used by the initiative transmission means may be selected at random.
The initiative transmission means may transmit, as its transmitting signal, at least one of a reply to a message from a user and a location registration signal.